In recent years, various polyester resin compositions have been employed for the production of molded articles. However, conventional polyester resin compositions have the respective disadvantages depending upon the main component contained therein. For example, in the case of polyester resin compositions composed mainly of a polybutylene terephthalate resin, satisfactory molded articles with high surface glossiness cannot be obtained because of its too high crystallinity. Moreover, polyester resin compositions composed mainly of a polyethylene terephthalate resin exhibit a low rate of crystallization and require high mold temperatures above 120.degree. C., although molded articles with high surface glossiness but low dimensional stability can only be obtained. As disclosed in Japanese Patent Publication No. 50-33832, these characteristics can be improved to a certain degree by use of a polymer blend comprising a polyethylene terephthalate resin and a polybutylene terephthalate resin at particular proportions; however, such a polymer blend is unsatisfactory for attaining the compatibility of surface glossiness and moldability. Furthermore, as disclosed in Japanese Patent Publication No. 59-0698, the above characteristics can also be improved in cases where a glycidyl ether of poly(alkylene glycol) is blended with a polyethylene terephthalate; however, such a polymer blend has the disadvantage of having unsatisfactory moldability and more particularly of requiring high mold temperatures.